The present disclosure relates to impedance readouts for active pixel sensors (APS). An APS is an image sensor that contains an array (rows and columns) of active pixels that incorporate amplifiers. One example of an APS includes a source follower array, i.e., an array wherein the pixel circuitry incorporates a source follower amplifier. Active pixel sensors are used in digital imaging applications such as filmless x-rays and fingerprint scanning. Other specific applications include but are not limited to mammography, radiography, cardiac imaging, and radiotherapy imaging.